The GSM (Global System for Mobile Communication) system is one example of a TDMA (Time Division Multiple Access) radio system, where data transmissions to users are separated from each other in time (also in frequency, FDMA). User transmission is carried out in data bursts, wherein each burst contains user data and a training sequence in the middle of the burst. The training sequence is a sequence of bits known by a receiver. By using the training sequence, the receiver can, in a channel estimation process, determine the position of the actual user data (useful signal) in the burst and also determine the distortion caused by the transmission.
Received signal quality also deteriorates due to interference, which includes multiple access interference (MAI) caused by other users, thermal noise and interference caused by the signal itself due to multi-path propagation. Antenna array techniques have been applied so as to benefit from space diversity at the receiver.
MRC (Maximum Ratio Combining) is one way to combat the interference in the receiver. In MRC, the aim is to maximize the combination signal-to-interference ratio from signals received via several antenna branches. MRC is an optimum strategy when the interference is uncorrelated between the antennas. This is, however, seldom the case in real wireless cellular systems and thus IRC, assuming the presence of interference, gives generally better performance.
There still exists room for improvement for the performance of current IRC receivers.